The invention relates to channel reuse patterns in a mobile communications systems.
Mobile communications systems, such as cellular or personal communications services (PCS) systems, are made up of a plurality of cells. Each cell provides a radio communications center in which a mobile unit establishes a call with another mobile unit or a wireline unit connected to a public switched telephone network (PSTN). Each cell includes a radio base station, with each base station connected to a mobile switching center that controls processing of calls between or among mobile units or mobile units and PSTN units.
From the original advanced mobile phone system (AMPS) standard, additional wireless protocols have been developed and implemented. One such protocol is the time-division multiple access (TDMA) protocol, originally implemented as the IS-54 standard (EIA/TIA/IS-54) and later followed by the IS-136 standard (TIA/EIA-136) from the Telecommunications Industry Association (TIA). With IS-136 TDMA, each channel carries a frame that is divided into six time slots to support up to three mobile units per channel. If half-rate voice coders are used, then each channel may be time shared among up to six mobile units. Other TDMA-based systems include Global System for Mobile (GSM) communications systems, which use a TDMA frame divided into eight time slots (or burst periods).
Traditional speech-oriented wireless systems, such as the IS-136 and GSM TDMA systems, utilize circuit-switched connection paths in which a line is occupied for the duration of the connection between a mobile unit and the mobile switching center. Such a connection is optimum for communications that are relatively continuous, such as speech. However, data networks such as local area networks (LANs), wide area networks (WANs), and the Internet use packet-switched connections, in which communication between nodes on a communications link is by data packets. Each node occupies the communications link only for as long as the node needs to send or receive data packets. With the rapid increase in the number of cellular subscribers in conjunction with the rising popularity of communications over data networks such as intranets or the Internet, a packet-switched wireless data connection that provides access to the data networks, electronic mail, files in databases, and other types of data has become increasingly desirable.
Several packet-based wireless connection protocols have been proposed to provide more efficient connections between a mobile unit and a data network. One such protocol is the General Packet Radio Service (GPRS) protocol, which complements existing GSM systems. Another technology that builds upon GPRS that has been proposed is the Enhanced Data Rate for Global Evolution (EDGE) technology, which offers a maximum data rate of 384 kilobits per second (kbps) and complements both GSM and IS-136 TDMA systems.
Because of frequency spectrum limitations, the number of channels that may be allocated for such packet-based data services in a mobile communications system may be limited. A channel reuse plan (in which the group of channels are reused at regular distances) having a relatively few number of channels may cause interference problems because of reduced distances between cells or cell sectors. Allocating more channels for packet-based services to provide for higher channel reuse plans that offer more robust carrier-to-interference performance may not be feasible because of the possibility of displacing traffic channels in an existing circuit-switched system. Thus, a need exists for a channel reuse method and system that reduces the likelihood of problems associated with channel interference while allowing for reduced frequency spectrum allocation.
In general, according to one embodiment, a method for use in a mobile communications system includes allocating a plurality of channels each having a predetermined frequency to carry signals. A plurality of time groups are defined, and a channel reuse pattern is provided that is based on both channel frequencies and time groups.
Some embodiments of the invention may provide one or more of the following advantages. By providing a channel reuse pattern that is based on both channel frequencies and time groups, a higher effective channel reuse is provided as compared to a reuse pattern based only on the number of channel frequencies. The higher effective channel reuse pattern allows for more robust carrier-to-interference performance, particularly for control signals, which are more sensitive to interference. By increasing the effective channel reuse, the number of channels that need to be allocated may be reduced, thereby reducing the frequency spectrum that needs to be allocated.
Other features and advantages will become apparent from the following description and from the claims.